Tests have been developed for the study of reticuloendothelial system function in man and have been widely applied to patients with autoimmune disease. Moreover, it has been found that defects in reticuloendothelial system function exists with patients with particular HLA types, namely HLA B8 DRw3, known to be associated with the development of autoimmune disease raising important questions as to the pathogenesis of the syndrome. Tests have now been developed to enumerate Fc receptor number on peripheral blood monocytes as well as average association constant of those Fc receptors. These tests are being applied to autoimmune disease patients as well as patients with a variety of other illnesses.